A Global Navigation Satellite system (GNSS) satellite-based navigation system may suffer from performance degradation when satellite signals are unavailable, blocked, attenuated and/or reflected. Example locations where the satellite-based navigation system suffer from performance degradation may include indoors and/or urban canyons.
The introduction of global positioning system (GPS) capability into smart phones has resulted in a high consumer demand for indoor and urban-canyon geo-location services. Since the performance of GPS by itself is poor in urban-canyon environments, other technologies are being developed to compliment or assist GPS for this important use case. One such technology is micro-electrical-mechanical system (MEMS) sensor based assistance. Some examples of such sensors are accelerometers, e-compass, gyroscopes and altimeters. A MEMS gyroscope may be implemented as a vibrating structure. A MEMS accelerometer may be implemented using a cantilever beam with a proof mass and incorporating a piezoelectric, piezoresistive or capacitive components for sensing. A tilt-compensated handheld electronic compass typically uses a dual-axis accelerometer as a tilt sensor, electronically gimbaling X, Y and Z magnetic field sensors. Magnetic field sensors require a horizontal orientation to the earth's surface at all times; therefore tilt data provided by an accelerometer or accelerometer+gyroscope is required for detilting e-compass measurements in order to get horizontal field components, when the e-compass is arbitrarily oriented, such as when a device is being carried by a user.
Sensor information has been shown to help GPS provide a more accurate navigation solution in urban canyon environments, e.g.: Gamini Dissanayake, et al, “The aiding of a Low-cost Strap-down Inertial Measurement Unit Using Vehicle Model Constraints for Land Vehicle Applications”. This is typically done by first deriving an INS (inertial navigation solution) fix from sensor information with some calibration assistance from GPS, followed by a blending of the INS solution with the GPS solution to get a more accurate position fix.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.